1. Field of the Invention
The invention relates to lancets and more particularly to a blood lancet with a protective movable cover for the lancet tip that is lockable into a tip covering position.
2. Description of Related Art
Many patient illnesses, such as diabetes, require the patient to take a small sample of blood for analysis purposes. Typically, this blood sample is obtained by pricking the patient's skin so that a drop of blood is produced. The patient's skin is typically pricked by means of a lancet. Originally these lancets consisted of a sharp pointed object that was manually pushed through the patient's skin creating a small wound through which the blood drop would flow.
A problem with such lancets is that the sharp lancet tip, after piercing the patient's skin, is exposed and therefore able to accidentally reprick the patient or others. For this reason, lancets having caps that cover the exposed lancet tip before use have been developed. In these devices, the cap may be replaced over the lancet tip after use to prevent inadvertent contact with the sharpened lancet tip. Examples of such devices are U.S. Pat. No. 3,358,689 issued to J. L. Higgins on Dec. 19, 1967; U.S. Pat. No. 4,635,633 issued to D. R. Hufnagle on Jan. 13, 1987; and, U.S. Pat. No. 4,712,548 issued to H. Enstrom on Dec. 15, 1987.
A problem with these devices is that, although the lancet tip is covered by the cap when it is in place, the lancet tip is exposed if the cap is inadvertently dislodged from its protective place. Consequently, it is desirable to produce a lancet having a lancet tip that is not exposed after use and that may not be inadvertently exposed after use.
Another approach to preventing accidental contact with the sharpened lancet tip has been to bias the lancet tip in a non-exposed position before and after use. The bias is usually accomplished by means of a spring. When the patient desires to draw a sample of blood, the bias of the lancet tip is overcome thereby exposing the lancet tip which contacts the patient's skin so that a drop of blood may be drawn. Thereafter, the bias moves the needle into a retracted position. Examples of this type of blood lancet are U.S. Pat. No. 3,338,239 issued to J. W. Mausteller on Aug. 29, 1967; U.S. Pat. No. 4,379,456, U.S. Pat. No. 4,503,856, and U.S. Pat. No. 4,580,565, issued to Cornell et al. on Apr. 12, 1983, Mar. 12, 1985, and Apr. 8, 1986 respectively; U.S. Pat. Nos. 4,676,244 and 4,738,261 issued to H. Enstrom on Jun. 30, 1987 and Apr. 19, 1988, respectively; and, U.S. Pat. No. 4,976,724 issued to R. L. Nieto et al. on Dec. 11, 1990.
A problem with this type of device is that the devices are relatively complicated and difficult to manufacture. In view of this, it is desirable to produce a lancet that is relatively simple and inexpensive to manufacture.
Another problem with these devices is that, although the lancet tip is retracted before and after use, after use, the lancet tip may inadvertently be re-exposed by inadvertently overcoming the bias holding the lancet tip in the retracted position. When the lancet tip is re-exposed, inadvertent contact may occur. This is a situation to be avoided.
Additionally, recent medical research has found that for many purposes, blood sampled from a patient's capillaries is desired. Typically, capillary blood is obtained from skin tissue near the skin's surface. Consequently, it is desirable to limit the depth of penetration of a lancet tip into a patient's skin in order to obtain capillary blood instead of arterial or venous blood that issues from lancet tip pricks that penetrate deeper into the patient's skin.
The thickness of a patient's skin varies due to factors such as age, health and the presence of callouses. As a result, each patient has a minimum lancet tip penetration depth necessary, at the point where a lancet prick is to be taken, to penetrate the skin sufficiently to allow an adequate amount of blood to be collected. Medical studies have shown that it is desirable to minimize the depth of penetration of a lancet tip into a patient's skin in order to minimize the pain or discomfort caused by the lancet prick. Therefore, it is desirable to provide a lancet that applies the lancet tip to penetrate the skin to the minimum lancet tip penetration depth so that an adequate amount of blood can be collected but also prevents the lancet tip from penetrating the skin further than this minimum penetration depth in order to minimize the pain or discomfort of the lancet tip prick.